1. Field of the Invention
The present invention relates to a method for preparing nano-carbon and nano-carbon prepared by making use of such method, and a composite material or mixed material containing nano-carbon and metal particles, an apparatus for preparing nano-carbon, a method for patterning nano-carbon and a nano-carbon base material patterned by making use of such method, and an electron emitting source using such a patterned nano-carbon base material.
The present invention is particularly suitable for a process for preparing an electron emitting source composed of particles in nano-scale (10xe2x88x926 to 10xe2x88x929 m) made up of carbon as a main component or a gas storage material, for example hydrogen storage material.
2. Description of the Prior Art
An explanation is given below for an electron emitting source:
A field electron emitting source has properties of energy saving and long service life, compared with a thermal electron emitting source requiring heating. At present, materials for field electron emitting source include a semiconductor such as Si (silicon), metal such as Mo (molybdenum), W (tungsten) and the like, carbon material in nano-scale size represented by carbon nano-tube (hereinafter referred to as xe2x80x9ccarbonaceous nano-materialxe2x80x9d). Above all, a carbonaceous nano-material has sufficient size and sharpness for concentrating electrical field and is relatively stable chemically and excellent in mechanical strength, and therefore, has a good prospect for a field electron emitting source.
A conventional method for preparing a nano-tube, a typical carbon nano-material, includes a laser abrasion method, an arc discharge method between graphite electrodes in an inert gas, a CVD (Chemical Vapor Deposition) method using hydrocarbon gas and so on. Particularly, a nano-tube prepared by an arc discharge method is suitable for a field electron emitting source for few defects in an atomic arrangement.
A process of a conventional arc discharge method is described below:
After placing oppositely two graphite electrodes in a container, the container is evacuated, and then, an inert gas is introduced into the container to generate arc. An anode irradiated with arc is evaporated vigorously to produce soot which is deposited on the surface of a cathode. After continuing the arc discharge for more than several minutes, an apparatus is opened to atmosphere and deposits on the cathode are taken out. The deposits on the cathode are composed of a soft core containing a nano-tube and a hard shell containing no nano-tube. When graphite containing a metal catalyst is used as an anode, a nano-tube exists in soot. A nano-tube is taken out of the soft core or soot, which is supported on a substrate and used as an electron emitting source.
Problems encountered by a carbonaceous nano-material such as a nano-tube according to a conventional arc discharge method and a method of preparing an electron emitting source made of the carbonaceous nano-material are as follows:
A vacuum container, a vacuum exhaust system and an inert gas introducing apparatus are required at the time of producing a nano-material, and the cost of apparatus is relatively high. Exhaust and open to atmosphere have to be repeated and process is long. Since recovery of the deposits on a cathode or recovery of soot and cleaning of the apparatus must be carried out every time after completion of the process, the conventional method is not suitable for continuous mass production. In addition, many processes such as separation of soft core and hard shell, isolation from soot, purification, supporting on a substrate and so on are required in order to make an electron emitting element by making use of the carbonaceous nano-material prepared by such method.
An object of the present invention is to provide a method of preparing nano-carbon comprising evaporating a material containing carbon as a main component by means of arc discharge which does not necessarily require a process container and so on, but uses an apparatus having a welding arc torch or an analogous structure to generate nano-carbon-containing soot and recovering the soot, and to provide an apparatus for preparing the same.
Another object of the present invention is to provide a method of preparing an electron emitting source in which nano-carbon acts for an electron emitting source, comprising supporting the soot on a substrate, and to provide an apparatus for preparing the same.
Further object of the present invention is to provide a method of recovering the soot comprising placing a base material in the surrounding area of discharge or in the surrounding area of scattering of thesoot, recovering the soot deposited on the base material through the base material, and to provide an apparatus for preparing the same, so as to make production and recovery easy. Similarly, still further object of the present invention is to provide a method of recovering soot comprising placing fluid (liquid) in the surrounding area of discharge or in the surrounding area of scattering of soot, and recovering the soot dispersed and dissolved in the fluid through the fluid, and to provide an apparatus for preparing the same. Similarly, still further object of the present invention is to provide a method of recovering soot comprising placing a particulate material in the surrounding area of discharge or in the surrounding area of scattering of the soot, and recovering the soot deposited or dispersed in the particulate material through the particulate material, and to provide an apparatus for preparing the same.
In addition, the recovered nano-carbon or composite soot containing nano-carbon and metal fine particles (composite material) can be used as a hydrogen storage material.
These and other objects of the present invention can be achieved by the aspects of the present invention described below.
A first aspect of the present invention, there is provided a method of preparing nano-carbon comprising the steps of placing a first electrode opposite to a second electrode containing a carbon material as a main component in atmosphere or air; applying voltage between the first electrode and second electrode to generate arc discharge; evaporating the carbon material of the second electrode by said arc discharge to generate soot containing nano-carbon; and recovering the soot containing nano-carbon.
In the method of the first aspect of the present invention, the first electrode is a torch electrode mounted to an arc torch, and the method is provided with a step of generating nano-carbon-containing soot by evaporating the carbon material of the second electrode by the arc discharge while making relative movement between the torch electrode and the second electrode.
In the method of the first aspect of the present invention, a base material is placed opposite to the arc discharge-generating area, and the method comprises a step of recovering the nano-carbon-containing soot through the base material.
In the method of the first aspect of the present invention, fluid or particulate material is placed opposite to an arc discharge-generating area, and the method comprises a step of recovering the nano-carbon-containing soot through the fluid or particulate material.
In the method of the first aspect of the present invention, an angle which the first electrode forms with the second electrode is in the range of 45 degrees to 135 degrees.
In the method of the first aspect of the present invention, the soot material comprises a single layer carbon nano-tube, carbon nano-horn, multi-layer carbon nano-tube, carbon nano-fiber, carbon nano-particle, CN nano-tube, CN nano-fiber, CN nano-particle, BCN nano-tube, BCN nano-fiber, BCN nano-particle, fullerenes, or mixture thereof.
In the method of the first aspect of the present invention, the soot is a composite or mixed soot comprising nano-carbon and metal fine particles.
In the method of the first aspect of the present invention, the carbon material of the second electrode is graphite or activated carbon or amorphous carbon, additive-containing or additive-embedded graphite or activated carbon or amorphous carbon.
In the method described immediately above, the additive is Li, B, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Y, Zr, Nb, Mo, Rh, Pd, In, Sn, Sb, La, Hf, Ta, W, Os, Pt, or oxide or nitride or sulfide or chloride or sulfate or nitrate thereof or, mixture thereof.
In the method of the first aspect of the present invention, the arc discharge is operated by direct current or direct current plasma, and arc discharge of the second electrode is a cathode for arc discharge.
In the method of the first aspect of the present invention, the arc discharge is operated by alternating current or alternating current plasma.
In the method of the first aspect of the present invention, the nano-carbon-containing soot is generated by evaporating the carbon material in an edge or depression or projection of the second electrode by the arc discharge.
In the method of the first aspect of the present invention, the arc discharge is carried out while supplying specific gas or air into the arc discharge-generating area.
In the method of the first aspect of the present invention, the specific gas is rare gas such as Ar, He and so on, nitrogen gas, carbon dioxide gas, oxygen gas, hydrogen gas or mixed gas thereof.
In the method of the first aspect of the present invention, the first electrode contains as a main component high-melting point metal such as graphite, W (tungsten), Mo (molybdenum), or Ni (nickel) and so on.
According to a second aspect of the present invention, there is provided a nano-carbon prepared by making use of a method according to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a composite or mixed material comprising nano-carbon and metal particles prepared by making use of a method according to the first aspect of the present invention.
According to a fourth aspect of the present invention, there is provided an apparatus for preparing nano-carbon comprising: a pair of electrodes comprising a first electrode, and a second electrode containing as a main component a carbon material or an additive-containing carbon material, or a carbon material on the surface of which is formed an additive, being held in an atmosphere or air at a given interval; an arc generating means comprising an electric source for applying voltage between the first electrode and the second electrode to generate arc discharge by which the carbon material is evaporated to generate nano-carbon-containing soot; a means for supplying specific gas in an area generating arc discharge; and a recovering means for recovering the soot.
In the apparatus of the fourth aspect of the present invention, the first electrode is a torch electrode mounted on an arc torch; and the apparatus further comprises a means for moving the torch electrode relatively to the second electrode, and nano-carbon-containing soot is generated by generating arc discharge by applying voltage between the torch electrode and the second electrode while moving the torch electrode relaticely to the second electrode, thereby evaporating the carbon material in the edge or depression or projection of the second electrode.
In the apparatus of the fourth aspect of the present invention, the recovering means is fluid or particulate material; and the apparatus further comprises a container for the fluid or particulate material placed opposite to the arc discharge-generating area; and the nano-carbon-containing soot is recovered through the fluid or particulate material.
In the apparatus described immediately above, the fluid is water or liquid or oily fluid having fluidity below temperatures at which arc discharge is generated.
In the apparatus of the fourth aspect of the present invention, the apparatus further comprises a covering member for covering at least an arc-discharge-generating area generated between both electrodes of the first electrode and the second electrode.
According to a fifth aspect of the present invention, there is provided a method of patterning nano-carbon comprising the steps of: placing a first electrode opposite to a second electrode containing a carbon material as a main component in atmosphere or air; applying voltage between the first electrode and second electrode to generate arc discharge; evaporating the carbon material of the second electrode by the arc discharge to generate nano-carbon-containing soot; and placing a base material on the surface or upper portion of which is placed a mask having a patterned opening opposite to the arc discharge-generating area, thereby depositing the nano-carbon-containing soot on the surface of the base material corresponding to the opening.
In the method of the fifth aspect, the method further comprises a step of: placing the base material in fluid opposite to the arc discharge-generating area, thereby depositing the nano-carbon-containing soot on the surface of the base material corresponding to the opening.
According to a sixth aspect of the present invention, there is provided a method of patterning nano-carbon comprising the steps of: placing a first electrode opposite to a second electrode containing a carbon material as a main component in atmosphere or air; applying voltage between the first electrode and second electrode to generate arc discharge; evaporating the carbon material of the second electrode by the arc discharge to generate nano-carbon-containing soot; and placing a base material the surface of which has an adhesive layer opposite to the arc discharge-generating area, thereby depositing the nano-carbon-containing soot at least on the adhesive layer.
In the method of patterning nano-carbon according to the fifth or sixth aspect of the present invention, the first electrode is a torch electrode mounted on an arc torch, and the method further comprises a step for generating nano-carbon-containing soot by evaporating the carbon material in the edge or depression or projection of the second electrode by the arc discharge while moving the torch electrode relatively to the second electrode.
According to a seventh aspect of the present invention, there is provided a patterned nano-carbon base material by using the method according to the fifth or sixth aspect of the present invention.
According to an eighth aspect of the present invention, there is provided an electron emitting source characterized by using the patterned nano-carbon base material according to the seventh aspect of the present invention.